Powder sprayer with flexible blades



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FOWDER SPRAYER WITH FLEXIBLE BLADES 6v sheets-sheet s Filed April 23,1964 OOO I NVEN TOR. MWD/95M a. Wfl/45A Dec. 13, 1966 w. G. BUHLERPOWDER SPBAYER WITH FLEXIBLE BLADES 6 Sheets-Sheet 6 Filed April 23,1964 United States Patent O M' 3,292,046 POWDER SPRAYER WITH FLEXIBLEBLADES Warren G. Buhler, Westfield, NJ., assignor to Oxy-Dry SprayerCorporation, New York, N.Y., a body corporate of New York Filed Apr. 23,1964, Ser. No. 362,128 6 Claims. (Cl. 317-3) This invention relates topowder sprayers, and more particularly, to powder sprayer units capableof laying down a substantially uniform layer of fine particle materialupon a surface which is usually in the form of a moving web or sheet.

The prior electrostatic powder sprayers have usually included a powderbox, `a metering mechanism for dispensing the powder material at auniform rate, and apparatus which provides an electrostatic field tofree the powder particles from the metering mechanism and to dispersethe particles so that they fall by gravity to the surface belowproviding a uniform powder layer. The metering mechanism usuallycomprises a dispensing roller and a tangential wiping blade. Typically,this tangential wiping blade is fairly rigid and relatively wide so thatit can be disposed within the powder box and, in addition to performingthe metering function, also provide an unobstructed sloping surface fortunneling the powder toward the dispensing roller.

Although reasonable success has been achieved, there are neverthelessseveral disadvantages inherent in the prior structures. As a practicalmatter, it is virtually impossible to construct a perfectly straightwiping blade due to the molecular structure and stress patterns in theblade material. In order to obtain a reasonably straight blade, theblade would be creased longitudinally during fabrication. Thereafter,when the blade is installed, it is necessary to overcompensate byincreasing the blade pressure against the roller sufficiently to insurethat the wiping blade engages the dispensing roller throughout itsentire length. The increased blade pressure increases the requireddriving torque for the roller and as a result requires a larger drivingmechanism. Since the blade pressure cannot be controlled accuratelythroughout the length of the blade, variations -in blade pressure couldnot effectively be used as a means for varying the powder dispensingrate. Also, it was very diicult to operate with relatively high rollerspeeds since it was diicult to maintain adequate blade pressure at allpoints along the roller engaging blade surface. l

The fact that the wiping blades are pre-bent also creates a problemsince it is necessary to carefully package the blades in rigidcontainers after fabrication so that the blades are not bent out ofshape during storage and shipping. As a result, the packaging, storingand shipping' expenses were substantial. The pre-bent rigid wipingblades were also found diicult to install on location and not readilyadjustable to compensate for tolerances in the supporting structure oruneven wear. Furthermore, the fact that the wiping blades were disposedinside the powder box created numerous problems when attempting toreplace a worn out blade.

v An object of this invention is to provide a powder sprayer including awiping blade arrangement which overcomes the disadvantages experiencedwith prior structures.

Another object is to provide a powder sprayer utilizing flexible wipingblades which are not pre-bent and which can therefore be rolled up whennot in use to facilitate storing and handling and substantially reducethe required manufacturing accuracies.

Another object is to provide powder sprayers wherein the wiping bladesare secured to the outside of the pow- 3,292,046 Patented Dec. v13, 1966 ICC der box so that the blades can easily be replaced withoutdisassembling the sprayer unit or removing the sprayer unit from itsnormal installed position.

Another objectis to provide a powder sprayer utilizing relatively narrowwiping blades which are easily -adjustable to provide the desired bladepressure against the dispensing roller so thatfriction between theroller and the blade can be minimized and so that the proper meteringaction can be achieved throughout arelatively wide range of rollerspeeds. y

Another object is to provide a powder sprayer wherein the wiping bladeis easily adjustable with respect yto the dispensing roller so that thepressure against the roller can be varied as desired to compensate fortolerances in the supporting structures. and inaccuracies due to unevenwear.

Another object is to provide a powder sprayer wherein the wiping bladesare easily adjustable to control the dispensing rate and to attaincertain controlled uneven powder distributions when desired.

In addition to the powder box, dispensing roller, wiping blades, andelectrostatic field generating apparatus, powder sprayers usuallyinclude a pneumatic structure for creating an air curtain on each sideof the sprayer between the powder boxand the surface below receiving thepowder layer. This air curtain confines the powder material to the areabelow the roller and eliminates the effect of ambient air currents.

A further object of the invention is to provide an integral structurewhich both supports the wiping blades and provides an air curtain.

A still further object is to' provide a pneumatic structure for creatinga relatively uniform air curtain, which is located within the powder boxbut does not decrease the useful capacity of the powder box.

Another object is to provide a pneumatic structure having a relativelylarge plenum chamber which creates an air curtain which is substantiallyuniform over the entire length of the powder sprayer.

Still another object is to provide a pneumaticstructure which provides-asubstantially uniform air curtain and which also prevents accumulationof powder on external portions of the sprayer unit.

The manner in which the foregoing and other objects are achieved is setforth more fully in the following specification which describes a fewillustrative embodiments within the scope of this invention. Thedrawings form a part of this specification wherein:

FIG. 1 is a perspective view, with portions broken away, illustratingone end of the powder sprayer;

FIG. 2 is a perspective view illustrating the other end of the powdersprayer with the journal structure partially disassembled;

FIG. 3 is a plan view of the powder sprayer and associated drivingmechanism;

FIG. 4 is a side view of the powder sprayer;

FIG. 5 is an end view of the powder sprayer taken. along line 5 5 asindicated in FIG. 4;

FIG. 6 is a cross sectional view of the powder sprayer taken along line6 6 as indicated in FIG. 4;

FIG. 7 is a longitudinal cross sectional view of the powder sprayerillustrating the journal structure and taken along line 7 7 as indicatedin FIG. 3;

FIG. 8 is an enlarged partial cross sectionalv view of the structureshown in FIG. 6 illustrating the details of the wiping blade assembly;

FIG. 9 is an illustration ofthe roller surface in accordance with oneembodiment of the invention as seen from line 9 9 in FIG. 8;

FIG. 10 is an illustration of an alternative surface structure for theroller as seen along line 9 9 in FIG. 8;

FIG. 1l is a cross sectional view illustrating the socket structure forretaining one end of a discharge tube;

FIGS. 12 and 13 arecross sectional views of one of the end bracketstaken along line 12--12 in FIG. 4 and illustrating the adjustabledischarge tube support structure; and

FIG. 14 is a cross sectional view similar to FIG. 8 but illustrating anIalternative wiping blade arrangement.

GENERAL DESCRIPTION The 'side panels for the powder sprayer inaccordance with this invention are constructed having sloping innersurfaces which lie in planes generally tangential to the dispensingroller so that all of the powder or dusting materials within the powderbox is funneled toward the roller. The outer surface of a side panel isvertical so that a triangular cavity` is formed within the panel toprovide a plenum chamber. A longitudinal V-shaped groove is machinedinto the lower horizontal portion of the side panel between the slopingand vertical surfaces. A plurality of holes are spaced along this grooveso that when air pressure exists within the plenum chamber a largenumber of air jets are provided along the groove. Due to the groove, thejets fan out elliptically and inwardly to thereby provide a relativelyuniform air curtain. The inwardly directionportion of these jets preventaccumulation of powder on the external surfaces of the wiper blade andassociated supporting structure.

The wiping blade is relatively narrow and is constructed from arelatively thin strip of blue spring steel. Preferably, the wiping bladeis coated with a liuorocarbon material. Thus, the wiping blade isflexible and therefore can easily be rolled up during storage andshipping.

The inwardly slanted surface of a side panel extends below the plenumchamber. This extended portion of the side panel is shaped to provide aretaining surface for the wiping blade. The wiping blade is securedbetween the retaining surface and a retaining strip by means oflongitudinally spaced adjusting screws. The retaining strip is shaped soas to deform the flexible wiping blade transversely of the roller overthe entire length of the blade or in other words, so that the wipingblade will take on a transverse S-shaped bend extending from one end ofthe blade to the other. As a result of this bend, the wiping bladebecomes relatively rigid and substantially straight in the longitudinaldirection. Since the blade is flexible, relatively narrow, and thesecuring structure is relatively close to the dispensing roller, theblade pressure against the roller can be accurately controlled by meansof the adjusting screws.

POWDER BOX, WIPER BLADES AND AIR CURTAIN First, referring to FIGS. 1-13an advantageous embodiment of the invention is illustrated wherein thepowder sprayer includes a powder box 1, defined by a pair of spacedapart side panels 2 and 3, end brackets 4 and 5 and a dispensing roller11. The side panels are secured between the end brackets by means of twopairs of support blocks 9 and 10, these support blocks being formed asAan integral portion of the end brackets. The side panels are secured tothe support blocks by means of suitable screws as illustrated. A spacermember 12 is secured intermediate the ends of the side panels and isflush with the upper edge thereof. A lid 6 is secured to the upper edgeof side panel 2 by means of an hinge 9 and is dimensioned to cover thetop of the powder box and wrap over'the upper edge of side panel 3 whenin the closed position. Dispensing roller 11 is journaled in the endbrackets and is disposed between the lower edges of side panels 2 and 3.

The side panels, best seen in FIGS. 1, 6 and 8, are preferably integralextruded aluminum panels. Side panel 3 includes a vertical outer portion14, a sloping portion 15 and a lower horizontal portion 16, whichportions dene a plenum chamber 17 having a generally triangular crosssection and extending through the side panel from end to end. Thesloping surface 15 lies in a plane tangential to dispensing roller 11and meets vertical portion 13 somewhat below the upper edge of the sidepanel. Surface 15 extends beyond the horizontal portion 16 and forms onesurface of a lower extended portion 18. The other flat surface ofextended portion 18 is blade retaining surface 19 which lies in a planewhich meets the plane of surface 15 at the point of tangency with theroller, or somewhat below the point of tangency. The plane dihedralangle between these planes is approximately 20 degrees. The lower edgeof extended portion 18 is rounded as shown.

A longitudinal V-shaped groove 25, best seen in FIG. 8, is machined intothe lower surface of horizontal portion 16. This groove forms an outervertical groove surface 26 and inwardly sloping groove surface 27.Preferably, the groove is located directly below the outer portion ofplenum chamber 17. A plurality of holes 28 are drilled through bottomportion 16 extending between the apex of groove 25 and plenum chamber17.

When the side panel is secured in position, end bracket 4 seals off oneend of plenum chamber 17, and end bracket 5 seals off the other end.Preferably, a sealing gasket is connected in position between the endbrackets and the side panels. A hose connecting nipple 29 is threadedinto a threaded bore 30 passing through end bracket 4 so as tocommunicate with plenum chamber 17. A suitable air pump can be coupledto the plenum chamber va an air hose (not shown) to create a pneumaticpressure within the chamber. As a result, a plurality of air jets areformed via holes 28. Because of groove 25, these jets tend to fan outelliptically and thus provide :a relatively uniform air curtainextending between adjacent holes throughout the entire length of theside panel. Due to sloping groove surface 27, a portion of each of thesejets is directed inwardly -to prevent accumulation of powder onretaining member 20, adjusting screws 22 and wiping blade 23 locatedbeneath the side panel.

Side panel 2 is identical to side panel 3 and includes components 33-49corresponding, respectively, to components 13-29 of side panel 3. Asshown in FIG. 6, the powder material to be dispensed is placed in thepowder box between sloping surfaces 15 and 35 and above dispensingroller 11. Thus, the sloping surfaces serve to funnel the powderdownwardly toward the dispensing roller. It should be noted that theplenum chambers are therefore located in an area which would otherwisebe wasted space. Plenum chambers 17 and 37 are suiciently large so thatthe air pressure therein is subst-antially uniform over the entirelength of the side panels.

Wiping blades 23 and 43 are each constructed from a thin, flexible stripof blue spring steel and are preferably coated with a lluorocarbonmaterial. These blades are approximately one inch wide and have a lengthequal to the length of the side panels 2 and 3. Holes are drilledthrough the blade near the upper edge and are spaced on tow inchcenters.

Semirigid retaining member 20, best seen in FIG. 8, is preferably anextruded aluminum strip equal in length to wiping blade 23 and sidepanel 3. Longitudinally spaced holes are drilled through retainingmember 20 corresponding in position to the holes in blade 23, andcorresponding tapped holes are drilled into extended portion 18 of sidepanel 3, these holes being normal t-o blade retaining surface 19. Wipingblade 23 is positioned between extended portion 18 of the side panel andretaining member 20, and this assembly is secured by means of suitable-round head adjusting screws 22. Preferably, the holes in t-he wipingblade, retaining member and extended portion of the side panel areaccurately aligned so that the wiping blade can easily be replaced.

Retaining member 20 includes a fiat blade engaging surface which curvesinto an inwardly extending-rib 21 at the lower edge thereof. Thedistance between screw 22 and rib 21 must be greater than the distancebetween screw 22 and the lower edge of extended portion 18. The distancebetween screw 22 and the upper edge 24 of the retaining member ispreferably somewhat greater than the distance along surface 19 betweenscrew 22 and the lower surface of bottom portion 16. Thus, when screw 22is tightened, moving retaining member 20 toward retaining surface 19,the upper edge 24 strikes the 'lower surface of bottom portion 16.Thereafter, when screw 22 is further tightened, retaining member 24pivots about edge 20 and applies pressure along-the longitudinal centerline of blade 23 via rib 21. As a result, the blade is bent inwardly byrib 21 along the center line of the wiping blade which is locatedbetween extended portion 18 and line of tangency on roller 11. Thus, thewiping blade is laterally deformed and takes lon an S-shaped bend asshown in FIG. 8. In this manner, the flexible blade becomes rigid. andsubstantially straight in the longitudinal direction. Each of the screws22 are separately adjustable, and hence, the pressure applied by thewiping blade against dispensing roller 11 can be adjusted as desired atselected points along the blade. This permits adjustments to compensatefor uneven wear or for tolerances in the dispensing roller surface orthe side panel. Also, it is possible to .adjust the blade so thatgreater pressure is exerted against the dispensing roller in selectedareas to thereby obtain a non-uniform dispensing rate when desired.

END BRACKETS AND DISCHARGE TUBE MOUNTING STRUCTURE End brackets 4 and 5are identical to one another and are secured abutting the ends of sidepanels 2 and 3 by means of support blocks 9 and 10 respectively which-form integral portions of the end brackets. The end brackets thus serveas closure members for the ends of the powder box and the ends of theplenum chambers Within the side panels. Also, the end brackets supportbearings for the journals for dispensing roller 11, arcuate surfaces forcooperating with the discharge tube supporting structure, and bracketportions ffor securing the powder sprayer to associated apparatus or asuitable support frame structure.

End bracket 4 is an integral structure including an end closure memberI60, a substantial circular -boss 61 extending horizontally yaway fromthe surface of closure member, and. a support leg 62 extendinghorizontally from the at surface of the boss. The diameter of circularboss 61 is approximately equal to the distance between the outersurfaces of side walls 2 and 3. Boss 61 is positioned to accommodate anolf-center journal housing 63 for discharge roller 11, the dischargeroller being located as shown in FIG. 12. The lower portion of closuremem ber 60, i.e., the portion lying below the horizontal center -line ofIboss 61, is curved and conforms lto the circular configuration of theboss. Support blocks 9 are secured to the edges of closure member 60 andextend in the direction of the side panels. Support blocks 9 are spacedapart so that they will lie on the outer surfaces of the side panelswhen the end bracket is secured in position. The upper edges of closuremember 60 and boss 61 are flush with the upper edges of side |panels 2and 3.

Support leg 62 can have any desired configuration and includes a vpairof slots 64 and 65 therein extending through the support leg from top tobottom. As shown in FIG. 7, support leg 62 is positioned slightly belowthe upper surface of boss 61 and. is strengthened by means of a taperedrib 66 extending from boss 61 along the upper surface of the supportleg. The support leg can be either horizontal as shown, or can bevertical to facilitate side mounting.

End support bracket 5 is an integral structure identical to end supportbracket 4 .and includes an end closure member 70, a substantiallycircular boss 71, a pair of spaced-apart support blocks '10, and asupport leg 72 with an associated strengthening rib 76 and slots 74 and75. Thus, when the end brackets .are secured in the positions as shownin FIGS. I and 2, the brackets close the ends of the powder box and alsoclose the ends of the plenum chambers within the side panels.Preferably, a sealing -gasket is cemented in position between the endbrackets and the ends of the side panels. As previously mentioned, apair of bores 30 and 50 Aare provided. eX- tending through end bracket 4and are each positioned to communicate with a different one of theplenum chambers 17 and 37 respectively. The threaded bores are 4adaptedto accommodate threaded. hose connecting nipples 29 .and 39respectively. End bracket 5 likewise includes a pair of threaded boresso that this end bracket will be identical to end bracket 4. Thethreaded bores in end bracket 5, however, are not used. and aretherefore sealed by means of suitable threaded plugs 77 and 78. Theassembled powder sprayer can be positioned as desired by means ofsuitable bracket members (not shown) bolted to support legs 62 and 72 orby bolting the support legs directly to a suitable supporting structure.

Discharge tubes 80 and 81 are similarly constructed and each includes acylindrical glass tube which is evacuated and then filled with an inertygas such as argon. The glass tubes are slightly longer than the sidepanels and are internally coated with a `suitable phosphorous material.The discharge tubes include a cathode at one end only. As shown in FIG.ll, the cathode end of the discharge tube includes a cup shaped cathodemember 82 connected to a conductive metallic end cap 83y by means of asuitable support conductor 84.

It is desirable that the discharge tubes be positioned generallyparallel to dispensing roller 11 and that they be adjustable in positionwith respect to the roller. Also, it is desirable that the tubes bedetachably secured so that they can easily be replaced.

The discharge tube support structure for tube 81 includes a support armhaving an arcuate inner surface with the same radius of curvature as thearcuate surface 91 at the periphery of boss 61. Thus, the inner surfaceof support arm 90 is adapted to engage arcuate surface 91 asshown inFIG. 1, and is adjustable with respect to the boss. Support arm 90includes an elongated locking slot 92 including an elongtaed annularshoulder 93 (best seen in FIGS. 12 and 13) which is concentric with thearcuate surface of boss 61. A tapped hole is bored into boss 61 alongthe horizontal center line and is dimensioned to accommodate a sockettype cap screw 94 which passes through slot 92. Thus, when cap screw 94is loosely placed in position, support arm 90 can slide from lan upperposition as shown in FIG. 12 to a lower position shown in FIG. 13. Itshould be noted that arcuate surface 91 is eccentric with respect to thedispensing roller surface due to the off-center location of the journalhousing with respect to boss 61. Support arm 60 can be rigidly secure atany position by tightening cap screw 94 so that the head of the screwengages shoulder 93 of the locking slot.

The lower portion of support arm 90 (as viewed in FIG. 1) is offset andis constructed to provide a bifurcated end portion 95 dimensioned toaccommodate a tab 96 extending from a spring biased tube socket 97. Asshown in FIG. 1l, a pair of axially aligned threaded apertures passthrough the leg portions of bifurcated end 95 and a smaller diameter,axially aligned, aperture passes through tab 96. A pair of socket type,headless, set screws 98 and 99 are threaded into the leg portions ofbifurcated end 95 so that the dog point ends of the set screws residewithin the aperture passing through tab 96. In this manner, socket 97 ispivotably secured to support arm 90 (as illustrated in FIG. 13) and canbe rigidly maintained in any desired pivoted position by appropriateadjustment of set screws 98 and 99.

A support arm 100, which is a mirror image of support arm 90, is'adaptedto engage the arcuate surface 101 located at the periphery of boss 71 ofend bracket 5. Support arm 100 is secured to end bracket 5 by means of acap screw 104 which passes through an elongated locking slot 102 andengages shoulder 103 within the slot. A tab 106 extending from a cupshaped tube socket 107 is pivotably secured to support arm 100 by meansof an oifset bifurcated end portion 105. Tube socket 107 is preferablyconstructed from a material having a high electrical resistance and isdimensioned internally to accommodate the end of electrostatic tube 81.

Spring biased socket 97 includes a generally cylindrical outer housing110 which is partially closed at one end. An insulated conductor 111passes through the partially closed end of housing 110 and through thecenter of a retaining washer 112. The free end of the conductor isimbedded in a globule or bead of solder 113 to provide a relativelylarge conductive surface and to prevent conductor 111 from pulling outof the washer. A spring 114 is disposed between retaining washer 112 andthe partially closed end portion of housing 110 to urge the retainingwasher away from the partially closed end of the housing. As previouslymentioned, tab 96, which extends radially from housing 110, is pivotablysecured by the bifurcated end portion of support arm 90. Housing 110 ispreferably an integral structure constructed from a material having ahigh electrical resistance.

Conductor 111 after emerging from the end of socket 97, is connected toone end of a high voltage secondary winding 115 of a transformer 116,the other end of the secondary winding being connected to a suitableground, which may be the side panels of the powder sprayer or a groundsurface located at some point below the sprayer. Primary winding 117 oftransformer 116 is connected to a suitable 60 cycle alternating currentsource. Transi former 116 is preferably constructed to provideapproximately 10,000 volts to electrode 82 via conductor 111.

Discharge tube 81 is installed by inserting the electrode end intospring biased socket 97 thereby compressing spring 114. The other end ofthe discharge tube is then inserted into socket 107, and when released,is retained in socket 107 by virtue of the force extended by spring 114.Thereafter, discharge tube 81 can easily be adjusted to any desiredposition parallel to dispensing roller 11 by means of the pivotable-connection between the sockets and support arms 90 and 100, or byadjusting the position of the support arms relative to end brackets 4and 5.

The adjustable support structure for discharge tube 80 is essentiallythe same as the supporting structure for discharge tube 81, except thatit is attached to position tube 80 on the opposite side -of dispensingroller 11. The components comprising the adjustable supporting structurefor discharge tube 80 are designated with reference numerals 120-144corresponding respectively to reference numerals 90-114. Conductor 141emerging from socket 127 is also connected to the ungrounded end ofsecondary winding 115 (FIG. 11).

ROLLER ASSEMBLY Roller 11 can be a solid steel roller with longitudinalextending shafts as shown in the drawings, or can include a hollowcylindrical roller with suitable roller gudgeons secured to the ends toform the longitudinal extending shaft portions. The length of the rollerportion is slightly less than the distance between end brackets 4 and asdetermined by the length of the side panels.

Journal shaft 150, extending from one end of roller 11, passes through ajournal opening 151 in end bracket 5 forming part of journal housing 73,and through a anged bearing 152 constructed from =a suitable bearingmaterial, preferably a iluoro-carbon material. Journal opening 151 isdimensioned to accommodate anged bearing 152 and includes an annularrecess dimensioned to seat the flange of the bearing. As shown in FIG.2, flanged bearing 152 is slid into position from outside end bracket 5and is thereafter secured to the end bracket by means of set screws \153passing through the ange of the bearing. An annular recess is alsoprovided on the inner side of end bracket 5 surrounding journal opening151, to accommodate a felt Washer 154 which provides :a journal seal andprevents powder from entering the bearing structure. A collar 155 isslid over the end of shaft 150 and is rigidly secured to the shaft bymeans of a set screw 156. This collar is positioned adjacent bearing 152and prevents longitudinal movement -of the roller with respect to theend bracket. A sprocket gear 157 is secured near the end of shaft 150 bymeans of a suitable set screw passing through the hub of `the gear. Asshownfin FIG. 3, a chain 158 couples sprocket gear 157 to an associatedsprocket gear mounted on the shaft of an electric motor 159. Motor 159is preferably of a variable speed drive type capable of rotating roller11 at speeds ranging from small fractions of one r.p.m. to fifty r.p.m.

Journal 63 in end bracket 4 is similar to journal 73 previouslydescribed and includes a flanged bearing 162 secured in a journalopening 161 by means of set screws 163 so that the bearing surroundsshaft 160 extending longitudinally from the end of roller 11. A feltsealing washer 164 is provided surrounding the shaft `on the inner sideof end bracket 4, and a collar 165 is secured t1o66shaft 160 adjacentbearing 162 by means of set screw The cylindrical surface of roller |11is advantageously coated with a uorocarbon material and thereafterfurther processed to provide a powder receptive surface. The processedsurface of the roller is illustrated in a magnified view of the rollersurface shown in FIG. 9 and includes an almost infini-te number of smallpowder carrying cavities. As illustrated in FIG. 8, the powder materialin powder box 1 is fed by gravity into the area between roller 11 andwiping blade 23. As the roller rotates, a thin layer of powder wedgespassed the wiping blade. The thickness of the powder layer, and hence,the quantity of powder dispensed, depends on the adjustment of screws 22which in turn determines the blade pressure against the roller. Theminimum rate at which powder can be dispensed is determined by thecapacity of the powder carrying vcavities and the minimum rotation speedof the dispensing roller. The dispensing rate can be increased by eitherincreasing the rotation speed of the roller or by decreasing the bladepressure against the surface of the dispensing roller.

An alternative surface stnucture for the dispensing roller isillustrated in FIG. 10 where the cylindrical surface is engraved topresent a uniform waflle-like pattern. This structure increases thecapacity of the powder carrying cavities which is desirable where highdispensing rates are required or large powder particles are beingdispensed. Preferably, the engraved dispensing roller -is coated with afluorocarbon material. With the dispensing roller surface shown in FIG.l0, the dispensing r-ate can also be varied by adjusting the speed ofrotation for the dispensing roller and the wiping blade pressure.

Although it has been mentioned that the dispensing rate for a givenroller surface can be adjusted by varying the roller speed and bladepressure, there is :a practical limit ot these adjustments sinceeventually the powder will begin to sift, that is, the powder will beginto come through in uneven chunks resulting in an uneven and relativelyuncontrolled powder distribution. The maximum dispensing r-ate for aparticular roller varies in accordance with the type of powder beingdispensed. When a particular roller does not achieve the desireddispensing rate, the roller is replaced with another roller havinglarger powder carrying cavaties.

It is significant that the roller yand the wiping blades are coated witha iluorocarbon material and that the roller bearings are likewiseconstructed from a -uorocarbon material. The fluorocarbon material msedfor coating the roller and wiping blades is preferably the polymer oftriiluorochlorenthylene commercially marketed under the tradename Kel-Fand characterized -by the formula (CF2--CFCl)x. First these materialsexhibit a high chemical resistance so that other materials, such as thepowder being dispensed, cannot readily :adhere to the roller and wipingblade surfaces. ySeco-nd, iluorocarbon materials have substantially azero moisture absorption characteristic and therefore reduced thepossibility of moisture contamination of the powder being dispensed.Third, these materials have a relatively high compression strength andhence, excellent wear characteristics. This is significant in thebearings, and also with respect to the roller and wiping bladearrangement which is subjected to the constant rubbing action as thepowder material, which may be abrasive, passes between the roller andwiping blade. Further, fluorocarbon materials have a high electricresistance and high resistance to electrostatic charges. It should benoted that the steel roller, due to the flanged fluorocarbon bearing andfluorocarbon coating is electrically isolated and hence, is electricallyinsulated from the electrostatic field. If the dispensing roller werenot isolated, there would be some electric charge, from theelectrostatic field created by discharge tubes 80 and 81, which would becarried into the powder box by means of the roller and therebyelectrostatically contaminate Vthe powder material. This electrostaticcontamination would adversely effect .the dispensing of the powdermaterial.

ASSEMBLY AND OPERATION The powder sprayer in accordance with thisinvention is of a generally symmetrical -design so as to minimize thenumber of different components. The side panel and wiping blade assemblyon one side of the roller is identical to the side panel and wipingblade assembly on the other side. The end brackets are identical to oneanother, and the two discharge tubes supporting structures are alsosubstantially identical. This symmetrical construction is alsoadvantageous since the dispensing roller can be rotated in eitherdirection and the entire unit can be installed with either side panelfacing outwardly.

The powder sprayer is installed with the dispensing roller positionedhorizontally, usually less than a foot above the surface to be coatedwith the powder material. Usuallyythe powder receiving surface is in theform of a moving web or sheet.

The powder or dusting material to be dispensed is either placed directlyin the powder box `above dispensing roller 11 or is supplied by asuitable feed mechanism. Thereafter, the drive motor is energized torotate motor 11. The roller, if rotating in a clockwise direction,rforces powder past wiping blade 23, in which case wiping blade 43 actsas la seal between the side panel and the other side of the roller. Onthe other hand, if the dispensing roller rotates in a counter clockwisedirection, wiping blade 43 provides the metering function and wipingblade 23 acts as the seal. In either event, the powder material ismetered out at a uniform rate. Thereafter, the force of gravity and theforce created by the electrostatic ield provided by the discharge tubes,strips the roller clean so that the powder material falls to the surfacebelow.

When discharge tubes 80 and 81 are energized, potential gradients arecreated surrounding the tubes which in turn ionize some of the airmolecules in the vicinity of the discharge tube. This eifect is known ascorona. The ionized particles having the same polarity as that appearingin the surface of the discharge tube stream away from the dischargetubes creating air currents referred to as electronic winds. Theseelectronic winds lare in a generally downward direction in the areabeneath dispensing roller 11. The downwardly directed electronic windand the electrostatic attraction of the power particles assist theforces of gravity in removing the particles from the roller. A largenumber of the released particles become charged with the same polarityas the surrounding air molecules. This effect creates a powder cloudbeneath the dispensing roller and brings about a more uniform disypersion of powder particles than could otherwise be achieved.

As previously mentioned, the dispensing rate is determined by therotational speed of dispensing roller 11, and the blade pressure againstthe dispensing roller surface. It should be noted that the wiping bladeis relatively narrow and that the retaining member, which controls theblade pressure, is relatively close to the dispensing roller. With thisarrangement the blade pressure can be controlled with considerableaccuracy. Furthermore, since the adjusting screws are individuallyadjustable, the blade pressure can be adjusted separately indiferentselected areas.

After the powder sprayer unit is placed in operation, the powderdistribution is observed and the roller speed and blade pressure areadjusted until a desired dispensing rate is achieved. If the powderdistribution is uneven, as may be caused by inaccuracies in thedispensing roller or side panels or by uneven wear, this is easilycorrected by adjusting the blade pressure in appropriate selected areas.In cases where a particular uneven distribution is desired, for example,more powder in the center than at the ends, such uneven distribution canbe attained by adjusting the blade pressure so that it is greater at theends than at the center.

The position of the discharge tubes can be adjusted so that one or bothof the tubes are effective, land hence, the effective strength of theelectrostatic eld can be varied over a relatively wide range. Also, thetube position can be adjusted to provide Aan electrostatic eld which isnon-symmetrical and which thus tends to propel powder particles in otherthan a directly downward direction. The non-symmetrical field can beused, for example, to compensate for the eect of ambient air curtains onthe powder particles as they fall from the dispensing roller to thesurface below.

When the unit is placed in operation, a pneumatic pressure is created inthe plenum chambers by means of a suitable air pump to thereby create anair curtain on each side of the roller. These air curtains extendbetween the side panels and the surface below and thereby protect theenclosed area from ambient air currents.

ALTERNATIVE BLADE ARRANGEMENT Another arrangement for positioning a.flexible wiping blade tangential to the dispensing roller is shown inFIG. 14. Roller 11 andfside panel 3 as shown in FIG. 14 are the same asthose previously described.

The flexible wiping blade is preferably constructed from blue springsteel and coated with a fluorocarbon material. The wiping blade isrigidly secured between retaining surface 19 of the side panel and arigid retaining strip 100. The retaining strip is securely fastened tothe side panel by means of screws 181 which pass through the retainingmember and the blade and which are then threaded into extending portion18 of the side panel.

Retaining strip extends beyond the lower surface of extended portion 18.A large number of adjusting screws 182 are spaced along strip 180. Thesescrews pass through the retaining strip and extend beyond the retainingstrip so that they engage wiping blade 183 in the area between the areasengaging the dispensing roller and the `retaining surface. Screws 182are extended so that the wiping blade becomes laterally deformed takingon 4an S-shaped bend. Adjustment of screws 182 controls the bladepressure against the dispensing roller.

Although only a few illustrative embodiments of the invention have beendescribed in detail, it should be obvious to persons skilled in the artthat there are numerous additional variations and embodiments within thescope of this invention. The invention is more particularly defined inthe appended claims.

What is claimed is: i 1. In an electrostatic powder sprayer, thecombination of a pair of spaced apart end members;

a cylindrical dispensing roller journaled between said end members;

receptacle means located between said end members and `above said rollerproviding a receptacle for powder materials to be dispensed;

means attached to said receptacle means for providing a retainingsurface near said roller and parallel to the axis thereof;

at least one wiping blade disposed to engage said retaining surface andto tangentially engage said dispensing roller, the combination of saiddispensing roller and said blade providing a metering mechanism fordispensing powder material lfrom said receptacle; first blade deformingmeans contacting that portion of said blade between said retainingsurface :and said dispensing roller and urging said blade toward saidroller to provide a first curvature of said blade extending uniformlyover the length of said blade;

second blade deforming means contacting that portion of said bladeextending beyond said retaining surface prior to deformation and urgingsaid portion of the blade toward said roller to provide -a secondcurvature extending uniformly over the length of said blade;

said first and second curvatures creating a transverse S-shaped bendextending over the length of said blade to provide rigidity of the bladeand resilient engagement with said roller.

2. A power sprayer in accordance with claim 1 wherein said rst andsecond deforming means are both part of a rigid blade deforming membermovable toward said retaining ysur-face to curve said blade around aportion of said retaining surface and to urge said blade beyond thepoint of mere engagement with said roller to thereby create saidS-shaped bend.

3. A powder sprayer in accordance with claim 2 further comprising aplurality of adjusting screws spaced apart along the length of saidblade deforming member, each of said screws passing through saiddeforming member and said blade and threaded into said retaining surfacefor adjustably urging said deforming member toward said roller.

4. In an electrostatic powder sprayer, the combination of a pair ofspaced apart end members;

means located between said end members dening a receptacle for powdermaterials;

a metering mechanism communicating with said receptacle for dispensingthe powder material at a substantially uniform rate, including acylindrical dispensing roller journaled between said end members withinan opening beneath said receptacle, and

at least one wiping blade tangentially engaging said roller;

means secured to said receptacle to provide a retaining surfaceextending parallel to the laxis of said roller, said blade beingdisposed to also engage said ,retaining surface so that said retainingsurface and said roller provide rigid support on lone side of said bladein two spaced apart areas;

deforming means on the other side of said blade initially contactingsaid blade in areas straddling the area of initial contact with saidretaining surface;

means urging said deforming means toward said dispensing roller tocreate a transverse compound bend extending throughout the length ofsaid blade; and

means for creating an electrostatic field in the vicinity of saiddispensing roller.

5. Apparatus in accordance with claim 1 wherein said dispensing rolleris provided with powder carrying cavities.

6, Apparatus in accordance with claim 4 wherein said means defining saidreceptacle includes a pair of spaced apart side panels secured betweensaid end members parallel to the axis of said roller, said side panelseach having sloping inner surfaces generally tangential to saiddispensing roller and at least one of said side panels being shaped toprovide said retaining surface.

References Cited by the Examiner UNITED STATES PATENTS 1,986,047 1/1935Dawley et al. 118-323 X 2,027,307 l/1936 Schacht 117-17 X 2,027,3081/1936 Schacht 117-17 X 2,394,657 2/1946 Beregh 95-1.7 X 2,972,332 2/1961 Limberger 95-1.7 X 3,114,482 12/1963 Dunaway 222-328 X 3,221,93812/1965 Yonkers et al 317-2 X MILTON O. HIRSHFIELD, Primary Examiner.

SAMUEL BERNSTEIN, Examiner.

I. A. SILVERMAN, Assistant Examiner.

1. IN AN ELECTROSTATIC POWDER SPRAYER, THE COMBINATION OF A PAIR OFSPACED APART END MEMBERS; A CYLINDRICAL DISPENSING ROLLER JOURNALEDBETWEEN SAID END MEMBERS; RECEPTACLE MEANS LOCATED BETWEEN SAID ENDMEMBERS AND ABOVE SAID ROLLER PROVIDING A RECEPTACLE FOR POWDERMATERIALS TO BE DISPENSED; MEANS ATTACHED TO SAID RECEPTACLE MEANS FORPROVIDING A RETAINING SURFACE NEAR SAID ROLLER AND PARALLEL TO THE AXISTHEREOF; AT LEAST ONE WIPING BLADE DISPOSED TO ENGAGE SAID RETAININGSURFACE AND TO TANGENTIALLY ENGAGE SAID DISPENSING ROLLER, THECOMBINATION OF SAID DISPENSING ROLLE AND SAID BLADE PROVIDING A METERINGMECHANISM FOR DISPENSING POWDER MATERIAL FROM SAID RECEPTACLE; FIRSTBLADE DEFORMING MEANS CONTACTING THAT PORTION OF SAID BLADE BETWEEN SAIDRETAINING SURFACE AND SAID DISPENSING ROLLER AND URGING SAID BLADETOWARD SAID ROLLER TO PROVIDE A FIRST CURVATURE OF SAID BLADE EXTENDINGUNIFORMLY OVER THE LENGTH OF SAID BLADE; SECOND BLADE DEFORMING MEANSCONTACTING THAT PORTION OF SAID BLADE EXTENDING BEYOND SAID RETAININGSURFACE PRIOR TO DEFORMATION AND URGING SAID PORTION OF THE BLADE TOWARDSAID ROLLER TO PROVIDE A SECOND CURVATURE EXTENDING UNIFORMLY OVER THELENGTH OF SAID BLADE; SAID FIRST AND SECOND CURVATURE CREATING ATRANSVERSE S-SHAPED BEND EXTENDING OVER THE LENGTH OF SAID BLADE TOPROVIDE RIGIDITY OF THE BLADE AND RESILIENT ENGAGEMENT WITH SAID ROLLER.